[libre-riscv-dev] [Bug 358] New: new MCU-ALU test picked up RC / OE / CR handling issue

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Sat May 30 20:47:48 BST 2020


            Bug ID: 358
           Summary: new MCU-ALU test picked up RC / OE / CR handling issue
           Product: Libre-SOC's first SoC
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: CONFIRMED
          Severity: enhancement
          Priority: ---
         Component: Source Code
          Assignee: lkcl at lkcl.net
          Reporter: lkcl at lkcl.net
                CC: libre-riscv-dev at lists.libre-riscv.org
   NLnet milestone: ---

yippee!  a new unit test (test_alu_compunit.py) just picked up that
we are using rc from Decode2ExecuteType in the wrong way.  as RC and
OE are both of type "Data", the test needs to be on "rc_ok" enabled.

i think.

the symptoms: test_alu_compunit.py fails because CR0 is not being
outputted on OP_CMP.  as in: cr0.ok is not being set.

it's not being set because in CommonOutputStage:
        comb += self.o.cr0.data.eq(cr0)
        comb += self.o.cr0.ok.eq(op.rc.rc & op.rc.rc_ok) # CR0 to be set

op.rc.rc & op.rc.rc_ok is *zero*, and yet the test in test_output_caller.py
(and test_alu_compunit.py) is this:

    def check_extra_alu_outputs(self, alu, dec2, sim, code):
        rc = yield dec2.e.rc.data
        if rc:

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